In recent years, with the increase in storage capacities of recording media and the spread of broadband networks, there has become widespread a system in which digital contents are distributed by being recorded in recording media or via a broadband network. Note that the digital contents are generated by digitizing copyrighted works such as movie and music, and are hereinafter referred to just as “contents”. In such a system, copyrights of contents need to be protected, and playback and copying of the contents need to be restricted under the agreement with copyright holders of the contents. As a conventional art for protecting copyright works against unauthorized acts such as copying of the copyright works without permission of copyright holders thereof, there has been known a method using an encryption technique. Also, there has been known a method of recording a program in a recording medium in addition to a content, and implementing a virtual machine that is an execution environment of the program in a playback device for playing back the content recorded in the recording medium. This art is disclosed in the Patent Document 1. When the recording medium is inserted into the playback device, the playback device reads the program from the inserted recording medium, and executes the read program in an execution environment (virtual machine) included therein. The content recorded in the recording medium is protected based on the program. When the program is executed, the protection of the content is cancelled, thereby enabling playback of the content.
On the other hand, in the process of manufacturing commercial recording media (hereinafter, referred to as “ROM media”) having contents recorded therein, it is important to check the quality of the contents. It takes time to manufacture commercial ROM media. After frequent checking of the quality, the commercial ROM media are released in the market. Such commercial ROM media are generally manufactured by transferring the recorded contents to recording media such as R media and frequently performing the quality check of the contents and re-creation of the contents. Here, playback devices are capable of playing back both contents recorded in ROM media and contents recorded in R media. Also, it is impossible to judge whether a recording medium is an R medium manufactured for testing (quality check) in the process of manufacturing ROM media or an R medium manufactured by copying a ROM medium in an unauthorized manner. Accordingly, copyrights of contents might be infringed.    Patent Document 1: U.S. Pat. No. 7,058,284